Everyone's nutritional status differs from others.

Multivits are only as good as the manufacturer who makes them.

One can put in RDAs of most vitamins and some trace minerals, but larger requirements, tend to leave out things like magnesium.
The magnesium listed on many multivits is magnesium stearate and is a lubricant to enhance manufacture and is not soluble and therefore is not absorbed. So multivits do not supply magnesium or large amounts of calcium, as a rule. Some products say take 2 or 3 or 4 to receive what is on the label, and those types may have more in them. Magnesium and calcium bulk up any tablet/capsule and typically are given separately, because of the volume requirement.

Multivits can be unsafe. There have been accidents where too much selenium has been put into them, for example, causing poisonings.
http://www.bt.cdc.gov/agent/selenium...ements2008.asp

So really the manufacturer of any product should be looked at carefully. When mixing so many things together, errors can happen more easily. And we are even seeing major drug companies removing many products they make OTC here in US because of contamination by glass, or metal pieces. Novartis has taken Maalox and other things off the market because their plant was so contaminated (water supply)! J & J had contaminated Tylenol and Motrin liquids for babies! And it was a year or more to fix that one.

So nothing is completely safe, if one wants to get nitpicky about it. People USED to say brand names were best, but Novartis and J&J have had these enormous contamination recalls!

You are not going to find an omega-3 in a multivit.
You are not going to find THERAPEUTIC levels of B12 in them.
The B12 is often synthetic cyano anyway.

For people who don't eat properly a multivit can be useful, but it won't fix things for people with genetic errors in metabolism, alcoholism, or provide magnesium and calcium in useful amounts. And a person may not require all that is in one either.

Nothing is "perfect".

BTW, you can drop that potassium supplement. It is a waste of money.
You require 4,500 mg of potassium a day. Paying money for 200mg is rather ineffective. Choose foods high in potassium instead.